Development of computer software for statistical genetic analysis can be facilitated by the availability of software tools that can be used to 1) verify the algorithms, 2) determine empirical type I error rates, 3) determine the power of a test, and 4) to determine the robustness of a test with respect to failures of underlying assumptions. The Genometric Analysis Simulation Program (G.A.S.P.) is a software tool that can generate samples of family data based on user-specified models. Both trait and marker data can be generated. Data generated can be as simple as a single sample of random individuals, or as complex as thousands of samples of extended families with traits based on a linear combination of major locus, polygenic, common sibship environment and covariate components.